Each stop knows where to send it next because they keep a table of where to pass letters given a destination address.

每个站点都知道下一步要发送到哪里，因为他们保留了一个表格，其中列出了给定目的地地址后将信件传递到哪里。

That's bad, because both cities are going to look at the destination address, Missoula, and end up passing the message back and forth between them, endlessly.

这很糟糕，因为两个城市都将查看目的地地址 Missoula，并最终在它们之间无休止地来回传递消息。

However, IP is a very low level protocol – there isn't much more than a destination address in a packet's header, which is the metadata that's stored in front of the data payload.

然而，IP 是一种非常低级的协议——在数据包的标头中只有一个目标地址，这是存储在数据有效负载前面的元数据。